Although Crohn's disease (CD) is generally found in the ileum and/or colon, since the 1960s it has become evident that this chronic inflammatory disorder of unknown aetiology can affect the whole gastrointestinal tract from mouth to anus. In 0.5-13% of patients with ileocolonic CD the disease occurs in the upper gastrointestinal tract as well (i.e., from mouth through jejunum). With the radiological double-contrast technique, however, early signs of upper gastrointestinal CD may be detected in 20-40% of patients with ileocolitis. On the other hand, histologically evaluated biopsies from the lower oesophagus, body of the stomach, gastric antrum and the duodenal bulb of patients with Crohn's disease from whom the upper gastrointestinal tract is normal, according to X-ray or endoscopy may reveal lesions, which are considered to be pathologically diagnostic. Jejunal involvement occurs in 4-10% of patients with ileitis, ileocolitis or colitis. In early studies biopsies of apparently normal buccal mucosa from patients with Crohn's disease showed a significant correlation between the activity of the disease, as defined by the Crohn's Disease Activity Index, and the number of plasma cells containing IgM, suggesting a generalized activated humoral defence system during relapse. A diagnosis of Crohn's disease of the upper gastrointestinal tract can be achieved by combining recognition of clinical, roentgenographic, and endoscopic features. Provided that other causes of granulomatous involvement of the gastrointestinal tract can be excluded, non-caseating granulomas are generally accepted as the histological proof of Crohn's disease. When Crohn's disease does involve the upper gastrointestinal tract, there is nearly always concomitant disease in the small bowel or colon. Compared to patients with an ileocolonic localization, patients with Crohn's disease in the upper gastrointestinal tract more frequently have colic-like abdominal pain and/or cramps, nausea and anorexia as presenting symptoms and are younger at onset of the disease. Medical therapeutic principles are the same as for Crohn's disease elsewhere in the gastrointestinal tract. Absolute indications for surgical treatment are massive bleeding, progressive stenosis, and extensive fistula formation.